The invention relates to a high-draft drafting unit for a spinning machine having several drafting zones which are each delimited by two pairs of rollers formed of pressure rollers and bottom rollers and of which at least one is equipped with an apron guide containing a top apron and a bottom apron, the axial length of coverings of the pressure rollers and the apron width determining the working width of the pairs of rollers transversely to the travel direction of a sliver.
In the case of drafting units for spinning machines, the pressure rollers or top rollers are normally constructed to be identical so that, along the whole travel path through a drafting unit, essentially the same working width is obtained at each pair of rollers. Deviations may occur in the area of apron top rollers since the apron width is standardized. It may therefore happen that the top rollers of the aprons are held longer than the other top rollers so that unintentionally a larger working width will occur in the area of the apron guide than in the area of the feeding roller pairs and of the delivery roller pairs. For example, it is known from a sales manual of the firm SKF (Drawing Number ASp 11 123, Edition 2/73) to select, in the case of a drafting unit support with the designation PK 220, the feeding and delivery top rollers with a working width of 25 mm. The smallest width of an available apron (Drawing Number ASp 11 125, 1984), on the other hand, is 28 mm.
An object of the invention is to simplify a high-draft drafting unit of the initially mentioned type and thus reduce its costs.
This object is achieved in that the working width, in the travel direction of the sliver, is reduced in one or several steps by the fact that the axial length of the pressure rollers which follow and/or the apron width of the apron guide which follows is reduced in comparison to the preceding ones.
In this manner, an adaptation is obtained of the working width to the sliver which becomes finer as a result of the drafting. This results not only in the saving of materials with respect to the pressure rollers but also permits a higher specific loading along the respective nip line so that the overall loading of the pressure rollers may be reduced. With the same clamping effect as before, work can be carried out with a lower loading force. Weaker springs may be used while, in addition, the loading of the bearings is reduced. In addition, the power requirement of the drafting unit is reduced which is an important factor particularly in view of the high delivery speeds at the outlet of the high-draft drafting unit endeavored today.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.